Re: performance issue after upgrade to oracle 11.2.0.1 linux 32 bit.

> -
>
> Randolf: regarding the optimizer bug that was fixed in 11.2.0.1 which
> was related to ROWNUM and incorrect cardinality estimates, I was
> unable to force 11.2.0.1 to reproduce the incorrect cardinality
> estimates by changing the OPTIMIZER_FEATURES_ENABLE parameter to match
> a lower release number.  So, I guess that some fixes are buried deep
> in the code.  I even tried disabling some of the bug fixes without
> success.  This seems to imply that changing the
> OPTIMIZER_FEATURES_ENABLE to an older version may not always reproduce
> the old optimizer behavior, which is a bit unfortunate.
>

Yes, Jonathan blogged about an example of this in "FBI problem" ( http://jonathanlewis.wordpress.com/2007/11/18/fbi-problem/ ) But it's still usually worth a try, if just to narrow possibilities.

Also, just to clearly emphasize to the OP, it is recommended in a lot of places not to set OPTIMIZER_INDEX_COST_ADJ and OPTIMIZER_INDEX_CACHING, at least until testing shows they help - it's likely a mistake to keep the settings from earlier versions. See http://richardfoote.wordpress.com/2009/09/01/optimizer_index_caching-parameter/ for some idea of what to look for.

jg

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